This invention relates generally to machines and devices for handling paper money or bills, slips, chits, checks, and other sheet articles (hereinafter referred to as "sheets"). More particularly, the invention relates to an overlapping feed detection device for detecting the state of two or more sheets being fed or conveyed in mutually superposed or overlapped relation in a sheet-processing machine.
Among sheet-processing machines, there are those, such as a sheet dispensing machine, in which sheets are taken out, one sheet at a time, from a sheet storing section for receiving and storing sheets at a specific place, and, after a specific number of sheets thus taken out have been counted, these sheets are dispensed or otherwise sent out. When, in a machine of this character, two or more sheets in mutually overlapping state are taken out of the storing section, it is necessary to detect this overlapping state and prevent feeding or conveying of sheets in such overlapping state.
For this purpose, various kinds of overlapping feed detection devices in sheet processing machines of the above described character have heretofore been proposed, and some have been reduced to practice. In general, almost all of these known devices are of the type wherein one of two rolls for clamping sheets passed therebetween is supported in a manner to permit it to separate from and contact the other roll and is urged by a spring to press it against the other roll, and, when sheets are sent in an overlapping state of two or more sheets between these rolls, the spring-biased roll is forced to separate excessively from the other roll, this excessive separation being detected by a detector such as a microswitch.
In a known detection device of this type, however, excessive separating and contacting movements of the spring-biased roll due to extraneous causes even when there is no overlapping are detected directly by the detector as an indication of overlapping or are transmitted as vibration to the contacts of the microswitch. For this reason, or because of lagging of the instants of ON-OFF operations of the microswitch due to bouncing of the spring-biased roll at the time when even a single sheet is caught between or released by the rolls, a vibratory disturbance occurs in the detection signal transmitted from the microswitch. That is, a so-called waveform-breaking or switch-chattering phenomenon develops and gives rise to an unstable detection operation of the device, which has heretofore been a difficult problem.
Furthermore, because of the above described causes, a difference occurs between the actual value and the signal value of the length of the overlapped parts, whereby it has been difficult to determine the true length of overlap.
As a consequence of the unstable operation due to these causes, in the case of an after treatment of sheets fed in overlapping state such as, for example, rejection, sheets of a number which is greater than that necessary are unavoidably rejected. This has led to a great drop in performance in the sheet-processing operation.